Body Mass Index and Age Affect Maximum Mouth Opening in a Contemporary American Population

Purpose: Although a standard cutoff value of less than 35 mm in the maximum mouth opening (MMO) has been used to diagnose trismus, this value does not account for natural demographic variations. The present cross-sectional study investigated the effects of age, weight, height, body mass index (BMI), and gender on the MMO in a healthy, heterogeneous population. Materials and Methods: A volunteer sample from multiple sites in Cincinnati, Ohio, without any reported head and neck pathologies or current dental prostheses and with intact natural incisors were included. The main outcome measure was the average MMO. Key demographic information was collected from each participant. Multivariate regression analysis was completed on the factors of age, gender, weight, and height. One-way analysis of variance was completed for binned categories of BMI. Results: Data from 330 participants (age range, 18 to 86 years; mean, 42.13 ± 18.53 years; 171 men, 159 women) were collected. The range of MMO was 31 to 71 mm. Age, height, and weight were significant predictors of the MMO, and the final model accounted for ∼20% of the variation in the MMO [adjusted r², 0.208; F(3,326) = 29.731; P = .001]. On average, individuals with a greater BMI had a greater MMO (BMI, ≤25 kg/m², 50.57 ± 7.16 mm; BMI >25 but ≤30 kg/m², 51.58 ± 7.13 mm; BMI >30 kg/m², 53.53 ± 9.84 mm). Conclusions: In a heterogeneous population of healthy adults, natural variations in age, height, and weight significantly affected the MMO.